An aerobic, Gram-stain-negative, rod-shaped bacterium, designated strain CC-LY845(T), was isolated from the surface of rice straw in Taiwan. Cells were non-motile, and no flagellum was detected. Comparison of 16S rRNA gene sequences indicated that the strain was phylogenetically related to species of the genus Rhizobium, with closest similarity to Rhizobium pseudoryzae KCTC 23294(T) (97.6 %), R. rhizoryzae KCTC 23652(T) (97.0 %) and R. oryzae LMG 24253(T) (96.7 %); other species showed lower levels of similarity (<96.6 %). The DNA-DNA relatedness of strain CC-LY845(T) and R. pseudoryzae KCTC 23294(T) was 34.8��3.1 % (reciprocal value 39.2��2.2 %). Phylogenetic analysis based on the housekeeping atpD and recA genes showed that the novel strain could be distinguished from R. pseudoryzae KCTC 23294(T) (92.7 and 91.5 %, respectively) and other species of the genus Rhizobium. The temperature range for growth was 25-42 �XC, the pH range was 5.0-9.0 and NaCl concentrations up to 4.0 % (w/v) were tolerated. Strain CC-LY845(T) did not form nodules on four different legumes, and the nodD and nifH genes were not detected by PCR. The major fatty acids were C16 : 0 and summed feature 8 (C18 : 1�s7c/C18 : 1�s6c). The polyamine pattern of strain CC-LY845(T) showed spermidine and putrescine as major polyamines. The predominant quinone system was ubiquinone 10 (Q-10). The DNA G+C content was 68.3��2.4 mol%. Base on its phylogenetic, phenotypic and chemotaxonomic features, strain CC-LY845(T) is proposed to represent a novel species within the genus Rhizobium, for which the name Rhizobium straminoryzae sp. nov. is proposed. The type strain is strain CC-LY845(T) (= BCRC 80698(T) = JCM 19536(T)).